Commercially useful copper base alloys which possess a combination of high strength and high electrical conductivity are usually difficult to obtain because the methods and elements utilized to provide good strength properties, for example, usually do so at the detriment of the electrical conductivity of the alloys. From a number of approaches to the solution of this problem, two methods of achieving the combination of high strength and high electrical conductivity have been most readily utilized. The first method is determining and adjusting the elements to be alloyed with the base copper to provide inherent high strength and electrical conductivity properties in the resulting alloy system. Elements such as zirconium and chromium have been used in the past as additions to copper base alloys to provide the desirable strength-conductivity combination. Precipitation hardened alloys which contain chromium generally have lower electrical conductivity but higher strength than pure copper. The precipitation of zirconium in copper is known to give large increases in electrical conductivity to the base copper but only small increases in strength properties over the values for the solid solution of zirconium in copper.
Another method which has been utilized to provide the strength-conductivity combination in copper base alloys includes adjusting the homogenization, hot working, annealing and aging of the alloy to provide high strength properties to the alloy system without reducing the electrical conductivity of the system. An example of this approach may be found in U.S. Pat. No. 3,930,894, issued Jan. 6, 1976. This patent teaches a method of working phosphor-bronze copper alloys which includes a high temperature homogenization, hot and cold working, intermediate annealing and a final heat treatment to provide desired properties. The alloy system utilized in said patent may include chromium. This patent does not discuss treating precipitation hardenable copper base alloys which contain chromium as an alloying element.
The present invention is an attempt to overcome the shortcomings of the alloying element methods and processing method described above by treating chromium-containing precipitation hardenable copper base alloys so that not only the strength properties of said alloys are increased after treatment but the electrical conductivity properties are also increased.
Accordingly, it is a principal object of the present invention to provide a method of processing chromium-containing precipitation hardenable copper base alloys in such a manner so as to increase both the strength and electrical conductivity properties of the alloys.
Further objects and advantages of the present invention will become apparent from a consideration of the following specification.